The invention discloses a preparation method of a flame-retardant conductive paper/glass fiber composite. The method comprises the steps as follows: carbon oxide nanotubes are prepared and filled with nano silicon, silicon filled carbon oxide nanotubes are obtained and then added to a graphene oxide suspension, a mixed solution is obtained, conductive paper is further prepared and subjected to high-temperature curing composition with glass fiber prepreg, and the flame-retardant conductive paper/glass fiber composite is prepared. The prepared conductive paper has the strength of 15 MPa or above and the elongation at break of 1.5% or above. The maximum heat release rate of the prepared flame-retardant conductive paper/glass fiber composite is 190-210 kw/m<2> and is 35.7%-41.9% lower than the heat release rate of common flame-retardant conductive paper/glass fiber composites, and the flame-retardant performance is improved.